1. Field of the Invention
The present invention relates to an apparatus for performing a driving control of a rotary element to a plurality of rotating positions and, more particularly, to an apparatus for performing a driving control of a filter disk or the like which is used in a photographing system.
2. Related Background Art
In a photographing system for a color television, a filter disk having a plurality of conversion filters for color temperature, which is used upon photographing, is provided in many cases. The filter disk is rotated manually or by electrically driving to properly select the filter which is adapted for photographing conditions and the selected filter is attached to a photographing apparatus, so that the use proper for the photographing conditions is realized.
Among other photographing apparatuses, in a color photographing apparatus for broadcasting to which a high quality video image is especially required, the apparatus is constructed so as to have two filter disks in many cases in order to enable a fine correction to be realized.
As a filter disk apparatus provided for such a photographing apparatus, there is one as shown in FIG. 10. In FIG. 10, a rotatable filter disk 62 holds four temperature conversion filters 64a to 64d so that they are fitted to the disk. A motor 66 rotates the filter disk 62. A potentiometer 68 detects a rotating position of the filter disk 62. When the motor 66 rotates the filter disk 62, a rotation input unit of the potentiometer 68 rotates as much as the same rotation amount as that of the filter disk 62.
A command signal regarding a selection of a filter position is transmitted from an electric circuit of a television camera through a signal line 71. A change-over switch 72 selects any one of resistors VR1 to VR4 to be connected to one input terminal of a comparator 73 in accordance with the command signal transmitted via the signal line 71.
Each of the resistors VR1 to VR4 generates a voltage value having the same level as that of a voltage value that is outputted from the potentiometer 68 through a position signal calculation circuit 75 when each of the filters 64a to 64d is arranged on a photographing optical axis. A voltage signal from the position signal calculation circuit 75 is inputted to the other input terminal of the comparator 73.
Accordingly, when the filter disk 62 is driven to the filter position corresponding to the command signal, the comparator 73 compares the voltage value generated from the potentiometer 68 through the position signal calculation circuit 75 with the voltage value from any one of the resistors VR1 to VR4. A filter disk driving circuit 74 drives the motor 66 so that an output from the comparator 73 is equal to 0, thereby rotating the filter disk 62.
For instance, in a state where the filter 64a is arranged on the photographing optical axis, when the change-over switch 72 is switched to a connecting position with the resistor VR3 corresponding to the filter 64c in accordance with the command signal, an output corresponding to a difference between the voltage value (voltage value corresponding to the current filter position) outputted from the potentiometer 68 through the position signal calculation circuit 75 and the voltage value from the resistor VR3 is inputted to the filter disk driving circuit 74. The filter disk driving circuit 74 drives the motor 66 while there is a difference between those input voltage values and stops the motor driving at a time point when there is no difference between them.
In such an analog type filter position control using the potentiometer as mentioned above, however, since the voltage value (voltage value from each of the resistors VR1 to VR4) which is set in order to set each filter on the photographing optical axis is compared with the voltage value indicative of the current filter position from the potentiometer and the motor is controlled so as to equalize the two values, the filter disk cannot be rotated in a range other than an electric operating angle range of the potentiometer (namely, a slider, which rotates in an interlocking relation with the filter disk, can slide on a resistive element).
Therefore, in the above system, for example, in order to rotate the filter disk 62 from a rotating position to arrange the filter 64a on the photographing optical axis to a rotating position to arrange the filter 64d on the photographing optical axis, such a rotating path that the filter 64a is directly changed to one 64d (64axe2x86x9264d) in which a rotation amount of the filter disk 62 is minimized cannot be used but the disk 62 has to be rotated so that the filter is subsequently changed to another one (64axe2x86x9264bxe2x86x9264cxe2x86x9264d). That is, the system has such a drawback that it is impossible to perform a so-called near rotating control.
According to one aspect of this invention, there is provided a rotating position control apparatus having a potentiometer comprising a contact element rotating in accordance with the rotation of a rotary element and a resistive element on which the contact element slides, and a control unit for driving the rotation of the rotary element to a plurality of rotating positions on the basis of an output of the potentiometer, comprising: an insulator which is provided between both ends of the resistive element of the potentiometer and on which the contact element can slide; and a voltage setting circuit for setting a voltage of the insulator, wherein the control unit drives the rotation of the rotary element from the current rotating position to a target rotating position at a minimum rotation amount on the basis of the output of the potentiometer when the contact element slides on the resistive element and slides on the insulator.
Pursuant to another aspect of this invention, there is provided a rotating position control apparatus having a potentiometer comprising a contact element rotating in accordance with the rotation of a rotary element and a resistive element on which the contact element slides, and a control unit for driving the rotation of the rotary element to a plurality of rotating positions on the basis of an output of the potentiometer, comprising an A/D converting unit for A/D converting the output of the potentiometer, wherein the control unit determines a direction to rotate the rotary element from the current rotating position to a target rotating position at a minimum rotation amount by performing a logical calculation on the basis of a value obtained by A/D converting the output of the potentiometer through the A/D converting unit and a command code to instruct the rotating position of the rotary element.
According to still another aspect of this invention, there; is provided a rotating position control apparatus which has a potentiometer comprising a contact element rotating in accordance with the rotation of a rotary element and a resistive element on which the contact element slides, detects a position of the rotary element as an output of the potentiometer, compares the detected position with a target rotating position as a position to which the rotary element is moved, and moves the rotary element to at least three predetermined positions, comprising: an A/D converting unit for A/D converting the output of the potentiometer; a control unit for setting a predetermined control code to control the rotation of the rotary element every rotating area in which a difference obtained by comparing a value obtained by A/D converting a voltage value of the rotary element detected by the potentiometer with a value obtained by A/D converting a predetermined voltage value in the target rotating position lies within a predetermined range; and a control signal switching device for selecting a control signal to control the rotation of the rotary element on the basis of the control code, wherein the control unit controls a rotating speed and the rotating direction in which the rotation of the rotary element with a minimum rotation amount is obtained on the basis of the control code, determines that the rotary element reaches the target rotating position, and when the rotary element is rotated on the basis of the control code, controls the rotating speed of the rotary element so as to be slower as the position of the rotary element is closer to the target rotating position.
In accordance with still another aspect of this invention, there is provided a rotating position control apparatus which has a potentiometer comprising a contact element rotating in accordance with the rotation of a rotary element and a resistive element on which the contact element slides, detects a position of the rotary element as an output of the potentiometer, compares the detected position with a target rotating position as a position to which the rotary element is moved, and moves the rotary element to at least three predetermined positions, comprising: an A/D converting unit for A/D converting the output of the potentiometer;:and a control unit for allowing the A/D converting unit to A/D convert a detection value of the rotary element detected by the potentiometer to set the resultant value to a position table code and setting the target rotating position of the rotary element as a command table code, wherein the control unit drives the rotation of the rotary element in the predetermined rotating direction in which the rotation amount is minimized on the basis of the combination of values of the position table code and the command table code.